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Sodium based batteries are promising post lithium ion technologies because sodium offers a specific capacity of 1166 amp; 8197;mAh amp; 8201;g amp; 8722;1 and a potential of amp; 8722;2.71 amp; 8197;V vs. the standard hydrogen electrode. The solid electrolyte sodium beta alumina shows a unique combination of properties because it exhibits high ionic conductivity, as well as mechanical stability and chemical stability against sodium. Pairing a sodium negative electrode and sodium beta alumina with Na ion type positive electrodes, therefore, results in a promising solid state cell concept. This review highlights the opportunities and challenges of using sodium beta alumina in batteries operating from medium to low temperatures 200 amp; 8201; C 20 amp; 8201; C . Firstly, the recent progress in sodium beta alumina fabrication and doping methods are summarized. We discuss strategies for modifying the interfaces between sodium beta alumina and both the positive and negative electrodes. Secondly, recent achievements in designing full cells with sodium beta alumina are summarized and compared. The review concludes with an outlook on future research directions. Overall, this review shows the promising prospects of using sodium beta alumina for the development of solid state batteries

In industrial applications, filter materials are often chosen according to cost as well as their processing and thermomechanical properties, but rarely in terms of their behavior during filtration, which is largely due to there being insufficient information available on the influence of filter materials and surface quality on filtration behavior. In this study, the manufacture of functionalized Al2O3 nanofilters was investigated, along with their filtration performance in short- and long-term filtration trials. In addition, sessile drop tests were performed to measure the contact angle of the nanofunctionalized materials, and yielded an approximately 10 deg (11 pct) higher contact angle for nanocoated materials sintered at 800 °C and 1250 °C than for those sintered at 1600 °C and an approximately 23 deg (23 pct) higher contact angle compared to surfaces without a nanocoating. The filtration mechanism was assessed by means of Porous Disk Filtration Analysis (PoDFA) and Liquid Metal Cleanliness Analyzer (LiMCA) monitoring systems, as well as by analysis of the used and infiltrated filters using Scanning Electron Microscopy and Energy Dispersive X-ray analysis (SEM/EDX) technology. Both short-term and long-term filtration trials showed that the filtration behaviors of the reference and nanocoated filters were comparable. It was therefore determined that nanocoating of such filters with Al2O3 does not provide any improvement with regard to filtration performance.

Sustainable and low-cost technologies for carbon-based nanomaterials are required for wastewater treatment. Two graphitic precursors (graphite flakes and graphite powder) were tested to synthesize graphene-related materials using mechanochemical treatment. For comparison, chemical graphite oxide (GO imp) was synthesized. The pristine and final products were characterized by SEM-EDX, particle size distribution, elemental analysis, surface area, DTA-TG and Raman spectra. Oxygen/carbon ratios of the mechanochemical and chemical routes were detected by EDX and confirmed using elemental analysis. The surface area increased from ~1 up to 666 and 328 m2 g−1 for graphite flakes and graphite powder at 24 h of mechanochemical treatment, respectively. However, the surface area for GO imp reached 157 m2 g−1. The removal of methylene blue, acid orange 7 and bisphenol A with the mechanochemical synthesized graphite oxides reached >93.8% at 30 min. The adsorption mechanism is mainly governed by π − π interactions and hydrogen bonding.

The state-of-the-art technology of raw silver refining in a silver nitrate-based electrorefining process (Moebius-electrolysis) is accompanied by several disadvantages, both from a technological and from an ecological point of view. In addition, increasing concentrations of critical impurities from secondary sources, like palladium, in raw silver are a further challenge for the future of silver refining. Thus, there is strong motivation for the development of an adequate, alternative process of raw silver refining to substitute the existing Moebius-electrolysis. Due to its less environmentally toxic character and the high aqueous solubility of its silver salt, methanesulfonic acid (MSA) is a possible base chemical for the design of an efficient refining method based on leaching of raw silver followed by electrowinning, with less ecological and technological complications. In this paper the results of some fundamental investigations on the leaching of raw silver granules, containing approx. 94% silver, with methanesulfonic acid and hydrogen peroxide as an oxidation agent are presented. Agitation leaching experiments were conducted on a laboratory scale and the effects of the solid concentration, the hydrogen peroxide dosage and the temperature as leaching parameters were studied. The obtained results indicate that silver leaching yields of more than 90% are achievable with leaching at elevated temperatures of 65 °C or 80 °C, solid concentrations of 500 g/L and at a stoichiometric H2O2:Ag-ratio of 3:1. Increased solid concentrations greater than 500 g/L and elevated temperatures of 65 °C or 80 °C additionally improved the selectivity of the process regarding the leaching of Pd.

Na-β″-alumina is the commercially most successful solid electrolyte due to its application in ZEBRA and NAS® batteries. In this work, Li-stabilized Na-β″-alumina electrolytes were doped with 3d transition metal oxides, namely TiO2, Mn3O4, and NiO, in order to improve their ionic conductivity and fracture strength. Due to XRD and EDX measurements, it was concluded that Mn- and Ni-ions are incorporated into the crystal lattice of Na-β″-alumina. In contrast, TiO2 doping results in the formation of secondary phases that enable liquid-assisted sintering at temperatures as low as 1500 °C. All dopants increased the characteristic fracture strength of the electrolytes, 1.5 wt% of NiO doping proved to be most efficient and led to a maximal characteristic fracture strength of 296 MPa. Regarding the ionic conductivity, TiO2 doping showed the uppermost value of up to 0.30 S cm−1 at 300 °C. In contrast to the other dopants, TiO2 doping lowered the sintering temperature needed to obtain a dense, stable, and highly conductive Na-β″-alumina electrolyte suitable for applications in Na based batteries.

The results of solidification experiments with gallium in a square-based 220 x 220 mm 2 container under the influence of alternating and travelling magnetic fields are presented. Such experiments are relevant for the growth of multi-crystalline silicon ingots for solar cells using directional solidification. The time-dependent magnetic fields are generated by a system of two inductors supplied with alternating current. The axial temperature field for solidification is established by thermostat-controlled heat exchangers at the top and the bottom of the container. A new approach for a reproducible directional solidification process using a special seeding technique is presented. The melt flow and interface positions are measured in-situ during solidification by using ultrasound sensor arrays for a 2D flow mapping, and single ultrasound transducers for interface detection. The experiments reveal significant changes of the flow structure and the interface shape with decreasing melt height. The results are compared with numerical simulation and a setup-independent categorization of the observed flow structures is proposed. Conclusions for silicon growth processes are discussed.

The contact angles of two different systems, molten silicon and a eutectic Si-8 at. pct Zr alloy and their evolution over timeon vitreous carbon and polycrystalline silicon carbide (SiC) substrates were investigated at 1500°C under vacuum, as well as in argon using the sessile drop technique. The contact angle and microstructure of the liquid droplet/solid substrate interface were studied to understand fundamental features of reactive wetting as it pertains to the infiltration process of silicon and silicon alloys into carbon or C/SiC preforms. Both pure Si and theeutectic alloy showed good wettability onvitreous carbon and SiC characterized by equilibrium contact angles between 29° and 39°. Theeutectic alloy showed a higher initial contact angle and slower spreading as compared to that of pure Si. On vitreous carbon bothsilicon and the eutecticalloy formed SiC at the interface, while no reaction was observed on the SiC substrates.

The pyro-electro-catalytic induced generation of hydrogen gas is an environmentally friendly and sustainable way to convert excess thermal energy into a storable form. The main idea is to make use of spontaneous polarization of pyroelectric materials that can be altered by temperature changes. Thus, surface potential changes and subsequent electron exchange with surrounding molecules can be induced. In this work, a fundamental model to describe the behavior of a thermally excited pyroelectric material in pure water is developed. The model combines the fields of pyroelectricity, electrochemistry, diffusion and semiconductor theory. After derivation, it was used to explore some basic questions on pyro-electro-catalytic hydrogen production and the accuracy was tested with experimental data. The results show that p/εr has to be balanced depending on the temperature gradient to maximize the hydrogen production. The validation of the experimental data revealed good agreement.

The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 &deg, C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 &deg, C and 30 min). The conventional test yielded contact angles of around 92&deg, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157&deg, Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thickness between 10 &micro, m up to 50 &micro, m and consisted of Al, C, and O, however, with different ratios than the original Al2O3-C coating. Thermodynamic calculations based on parameters of the wetting and filtration trials underline the possible formation of an Al4O4C-layer.

In this work we present a carbon free gas diffusion electrode (GDE) design. It is a first step towards improvement of technologies like alkaline fuel cells, some alkaline electrolyzes and metal-air-batteries by circumventing carbon degradation. A nickel-mesh was made hydrophobic and subsequently electrochemically coated with MnOx as electrocatalyst. By this, a carbon free GDE was prepared. The contact angle, specific surface area (BET), pore size distribution, crystal phase (XRD) and electrochemical properties were determined. The deposition scan rate (r scan) during dynamic MnOx deposition altered the macro surface structure, pore size distribution and deposited mass. High catalyst masses with high specific surface area were achieved by lower r scan, but hydrophobicity was decreased. Impedance spectroscopy showed that higher MnOx mass will increase the ohmic resistance, because of the low conductivity of oxides, such as MnOx. The diffusion of dissolved oxygen is the major contributor to the total resistance. However, the polarization resistance was reduced by increased specific surface area of MnOx. It was concluded that the ORR and OER are limited by diffusion in this design but nevertheless showed reasonable activity for ±10 mA cm−2 corresponding to ~8 O cm−2 while references exhibited ~3.5 O cm−2.

A sustainable route to produce graphite oxide (GO) is presented using dry ball milling. The production method was based on pristine graphite flakes in a planetary ball mill. The prepared GO was characterized using UV–vis spectroscopy, BET surface area analysis, thermal analysis, SEM-EDX, TEM, XPS, elemental analysis, and Raman spectroscopy. The degree of graphite oxidation was controllable by the milling time and milling material, and the carbon-based yields ranged from 86 to 97%. The maximum oxygen/carbon ratios of the produced GOs were 0.16 and 0.15 after 24 h of ball milling with steel and zirconia balls, respectively. The BET surface area increased with increasing milling time from 1 m2 g–1 for pristine graphite up to 730 m2 g–1 for the ball-milled samples. Furthermore, the intensity ratios of the D and G bands (ID/IG) from the Raman spectra were 0.84 and 0.77 for GO produced with the steel and zirconia balls, respectively. The in-plane sp2 crystallite sizes (La) of graphite (168 nm) decreased to 20 (...

This paper describes novel equipment for model experiments designed for detailed studies on electromagnetically driven flows as well as solidification and melting processes with low-melting metals in a square-based container. Such model experiments are relevant for a validation of numerical flow simulation, in particular in the field of directional solidification of multi-crystalline photovoltaic silicon ingots. The equipment includes two square-shaped electromagnetic coils and a melt container with a base of 220×220 mm 2 and thermostat-controlled heat exchangers at top and bottom. A system for dual-plane, spatial- and time-resolved flow measurements as well as for in-situ tracking of the solid-liquid interface is developed on the basis of the ultrasound Doppler velocimetry. The parameters of the model experiment are chosen to meet the scaling laws for a transfer of experimental results to real silicon growth processes. The eutectic GaInSn alloy and elemental gallium with melting points of 10.5 °C and 29.8 °C, respectively, are used as model substances. Results of experiments for testing the equipment are presented and discussed.

Carbon Nanotubes (CNTs) have been oxidized with ozone in the gas phase and different Advanced Oxidation Processes (AOPs) in the aqueous phase such as H2O2/UV, Fenton reaction and ozonation, in order to functionalize them. A significant difference between the amounts and types of oxygen containing groups were generated using different oxidants. To investigate the efficiency of the oxidation methods, we monitored the depletion of the oxidants, using a titration of H2O2 with KMnO4 and an ozone analyzer for the ozonolysis experiments. Furthermore, we investigated the formation of hydroxyl radicals during the oxidation experiments by decolorization of methylene blue and depletion of salicylic acid. Boehm titration, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, temperature programmed desorption and thermogravimetric analysis have been utilized to characterize the CNTs. Our results demonstrate that direct ozonolysis with water vapor produces the highest amount of oxygen containing surface in comparison to the other oxidation methods, and this by using only a small amount of the available oxidant. With our results we confirm different previous assumptions about the oxidation mechanisms and theoretical calculations for oxidation processes practically.

NaNiCl2 batteries are member of the sodium metal halogenide battery family and represent a robust, save and environmentally friendly storage technology, which is in operation all over the world from small to large scale for decades. In particular, the high cycle stability, lifetime and the excellent safety predestine the technology for large scale stationary applications. Nevertheless, a significant marked penetration has so far failed to materialize. The dominating obstacle are the costs for conventional NaNiCl2 in competition with the dramatically falling prices for Li-Ion batteries. The energy intensive ceramic electrolyte manufacturing and the usually used high amount of nickel are mainly responsible. Beside this, some high power technical applications, such as peak shaving, are currently not accessible for NaNiCl2 batteries. The limited C-rates permit an economic operation of these business cases. To overcome these obstacles material scientific and engineering approaches are under development in workgroups all over the world. In the presentation, a technological review of new concepts for sodium metal halogenide batteries will be given. This will include new materials, designs and production methods along the battery value chain. The high economical impact from solid electrolyte manufacturing was tackled by lowering the sintering temperature by material doping. By 1.5 % TiO2 doping the sintering temperature for the Na-ß-alumina electrolyte was lowered by 150 °C. By optimizing the microstructure, an ionic conductivity of 0.25 S/cm and a mechanical toughness of 210 MPa were reached at the same time. Different cell designs matching different requirements in terms of power and energy will be presented. This will include 25 Ah plate cells and large tubular cells with high energy contents. Using the plate cell approximately, 100 % DoD can be discharged with an elevated current of 1 C which pushes NaNiCl2 close to Li-Ion cells. By a simple stacking of the cells, the capacity and the voltage level of a module can easily be adjusted to different applications. For high-energy applications tubular 100 Ah cells and 5 kWh battery packs were successfully developed. The simplification of the cell and module design with the simultaneous use of innovative production methods ended up in calculated costs of 300 to 400 €/kWh for a large scale production. An intermediate temperature NaNiCl2-like cell concept was developed. A fundamentally different cathode composition and a liquid sodium anode opens the door to a batteries with improved round trip efficiency, compared to high temperature NaNiCl2. Metal halogenid batteries have a high development potential. Away from the classic high temperature NaNiCl2 technology, a several approaches are under development and on the way to become a product in the near future. A successful implementation of the described approaches will yield in excellent batteries for large-scale stationary energy storage.

Verbrauchte nickelhaltige Nichtedelmetallkatalysatoren aus der chemischen Industrie, der Erdolraffination, der Lebensmittel- und Pharmaindustrie sind potenzielle Sekundarrohstoffe fur das Recycling von Nickel. Im Rahmen der Forschungsarbeit wurde ein Badschmelzverfahren fur nickelhaltige Katalysatoren entwickelt, die organische Reste der Fetthartung sowie Erdolraffination enthalten. Bei diesem Verfahren wird Nickelstein gebildet und weitere Wertmetalle wie Molybdan und Wolfram werden in eine verwertbare Schlacke uberfuhrt. Der Energiegehalt der organischen Verbindungen wird fur den Schmelzprozess genutzt. Damit wird eine erhebliche Energieeinsparung und Verringerung von CO2-Emissionen erreicht.

The anti-inflammatory drug diclofenac is found worldwide in natural water bodies and toxicological investigations report harmful effects for aquatic species even at low concentrations. Diclofenac is one of the pharmaceutical substances on the first watch list of the European Water Framework Directive. If it will be categorized as a priority substance, emission limits will be established. One of the discussed methods of diclofenac reduction in wastewater are advanced oxidation processes. In this paper, the degradation of diclofenac in water was investigated using a sonoelectrochemical system, consisting of an ultrasound transducer with a frequency of 850 kHz and boron doped diamond electrodes. With the combination of acoustic cavitation and electrochemical oxidation, as advanced oxidation processes, more than 90% of diclofenac could be degraded within 5 min at an initial concentration of 50 μg L−1. These studies provide optimization of ultrasound density, voltage and electrode positioning on diclofenac degradation. The reaction was found to follow pseudo first order kinetics with a rate constant of 0.505 min−1. Samples were concentrated with solid phase extraction and analyzed by high pressure liquid chromatography using a diode array detector. The formation of oxidative species was visualized by chemiluminescence of luminol.

The development of new filters for the aluminum industry requires investigations on the wettability of aluminum and its alloys on novel filter materials. The requested filter effects require not only an adequate wetting but also information about the interaction between the filter material and the metal. In the present work the wettability of an AlSi5Mg alloy on spodumene (LiAl[Si2O6]) containing substrates is investigated using the sessile drop technique. These measurements were carried out at 1223 K (950 °C) under vacuum. The spodumene-based substrates showed a completely different wetting behavior compared with an alumina substrate. The contact angel reduced more quickly and leveled out at a lower value (75 ± 2 deg) than in case of a pure alumina substrate (90 ± 1 deg). The reason for this behavior is a reaction between the LiAl(Si2O6) and the alloy droplet which supported deoxidation and formed a silica-rich reaction layer at the droplet/substrate interface.

The influence of the filter surface chemistry of alumina skeletons on the filtration effect was tested with five different oxide coating materials (Al2O3, spinel, mullite, TiO2, and SiO2). All prepared filters were casted successfully under industrial conditions. The casted aluminum samples showed no contamination caused by the filters. The evaluation of the casted filters by means of SEM and EDX showed that the amount of inclusions in the area of the run in is larger than in the middle and the run out of the filter. The most non-metallic inclusions were found in the casted filters Al2O3+Al2O3 and Al2O3+spinel. The wetting experiments yielded for all tested materials a non-wetting behavior whereby Al2O3 and spinel showed higher wetting angle than mullite, TiO2, and SiO2.

This paper presents an experimental study on the interaction between impurities, inclusions, and dislocations in multi-crystalline silicon ingots grown from well-mixed and poorly mixed melts. The ingots were grown in a high-vacuum induction furnace by the vertical Bridgman method and the degree of impurity mixing within the melt was modified by changing the growth rate. Vertical and horizontal slices were prepared from the ingots and analyzed by Fourier transform IR spectroscopy, as well as reflected-light and IR transmission microscopy to measure the axial carbon concentration and the distribution of dislocations or inclusions, respectively. The correlation between individual inclusions and dislocations has been investigated by correlative reflected-light/IR transmission and scanning electron microscopy. The influence of the melt mixing on the segregation of carbon is demonstrated and discussed with respect to the consequences for the formation of inclusions and dislocation clusters in multi-crystalline silicon.

Micropollutants are becoming an increasing problem for the environment and wastewater treatment. One example is Bisphenol A (BPA), an endocrinic disruptor, which is widely used in plastic production. Due to its endocrine disrupting effects on aquatic (micro-)organisms and it subiquity, in surface- and wastewater alike, adequate treatment techniques are necessary. In this study, the degradation of BPA by a sonoelectrochemical hybrid system was investigated, using a low frequency (24 kHz) ultrasound horn and two boron doped diamond electrodes. It was found that by the combination of the individual processes, i.e. ultrasound and electrochemical oxidation, more than 90% of BPA could be removed within 30 min at an initial concentration of 1 mg L−1. Moreover, synergistic effects were discovered and a considerable improvement compared to the individual processes could be achieved by using a potential of 5 V, whereas synergistic effects were absent at a potential of 10 V. This study provides investigation of ultrasound amplitude, potential and electrode positioning on BPA degradation. The reaction was found to follow pseudo first order kinetics with a rate constant of 0.089 min−1. Samples were analysed by high pressure liquid chromatography (HPLC) using a diode array detector. Moreover, the presence and distribution of hydroxyl radicals within the reactor was visualized by using sonochemiluminescence.

TiO2-based material is widely studied as a promising anode for rechargeable lithium ion batteries due to its unique properties such as high safety, easy handling and low production cost. On top of that, the high structural stability of TiO2 arises from the low volume expansion of less than 4% upon cycling, without Li dendrite formation or electrolyte decomposition that turns them into stable and safe anode materials. Nevertheless, the low ionic conductivity represents the main obstacle behind the low practical capacity of TiO2 electrode. Manufacturing of TiO2 nanostructures is one of the effective solutions to create short diffusion pathways for Li, to enhance the ionic conductivity by lattice defects and, finally, the electrochemical performance of titania. TiO2 nanotubes represent the ideal one-dimensional nanostructure, especially when they are aligned and perfectly arranged in close packed arrays with high surface area. Ordered TiO2 nanotubes are commonly synthesized by the anodic oxidation of titanium in fluoride ion-containing electrolytes [1]. However, the use of such an anodization bath requires complicated safety measures, due to its harmful impact on both health and the environment, which in turn is translated into a higher production cost. Despite several attempts have been reported to grow self-ordered TiO2-NTs in fluoride-free electrolytes, only bundles of interwoven and disordered tubular morphologies were formed [2,3]. Herein, we report the successful fabrication of vertically aligned and highly ordered TiO2-NTs by means of anodization in a fluoride-free aqueous electrolyte. The typical formation bath is composed of diluted sulfuric acid as electrolyte basis and chloride ions. Various synthesis parameters such as chloride concentration, pH, voltage, growth time, and temperature were explored to optimize the ideal fabrication conditions of the nanotubes. Structure, composition and morphology of the grown oxide tubes were investigated. The vertical alignment in an ordered porous nanostructure revealed from our results push the grown nanotubes into very promising position as candidates for lithium ion storage. The electrochemical performance of the NTs was evaluated vs. Li/Li+ without binder or conductive additives. The effect of the annealing temperature on the crystallinity and the lithium ion storage properties was investigated. The TiO2-NT electrodes demonstrated a reversible capacity of 150 µAh cm-2 after 50 charging/discharging cycles with a Coulombic efficiency close to 100% and without decomposition of the tubular structure at a current rate of 1C. The noticed cycling stability of the NT electrodes is attributed to the high structural stability of TiO2 and the perfect contact between the oxide films and the substrate which is utilized as a current collector. References [1] M. Madian, A. Eychmüller, L. Giebeler, Current advances in TiO2-based nanostructure electrodes for high performance lithium ion batteries, Batteries, 4 (2018) 7. [2] C. Richter, E. Panaitescu, R. Willey, L. Menon, Titania nanotubes prepared by anodization in fluorine-free acids, J. Mater. Res., 22, 6 (2007) 1624- 1631. [3] Y. L. Cheong, F. K. Yam, S.W. Ng, Z. Hassan, S. S. Ng, I. M. Low, Fabrication of titanium dioxide nanotubes in fluoride-free electrolyte via rapid breakdown anodization. J. Porous Mat., 22, (2015)1437–1444.

In this paper, an experimental study of dislocation structures in multicrystalline silicon is presented. The alignment of dislocations in samples from both edge-defined film-fed growth and ingot crystallization by vertical Bridgman growth is investigated. Crystallographic orientations of single grains and dislocation structures are analyzed by electron backscatter diffraction and infrared microscopy. { 111 } and { 211 } planes are identified to be the typical crystallographic planes, where dislocations are arranged. It is concluded that { 111 } and { 211 } planes are involved in plastic deformation and recovery processes during growth, respectively. In ribbon-grown samples, the dislocations are mainly arranged on { 111 } slip planes, whereas an arrangement on { 211 } planes prevails in ingot-grown samples. The influence of the growth and cooling conditions on the final alignment of dislocations in mc-Si is discussed and a possible explanation for a different annealing behaviour of ribbon- and ingot-grown crystals is given.

This paper presents an experimental study of the influence of the growth rate on the microstructure of multi-crystalline silicon (mc-Si). Crystals with a diameter of 105 mm were grown from an inductively heated, well-mixed melt by the conventional vertical Bridgman technique. Axial and vertical samples were prepared from the crystals to analyze the grain structure as well as the distribution of dislocations and precipitates. The results show that the growth rate influences the microstructure of the crystals mainly at the beginning of the solidification process. Growth with a low growth rate, for instance, favors the formation of radially elongated grains near the bottom of the crystal and suppresses the heterogeneous nucleation of SiC precipitates at the inner crucible wall. The effect on the grain shape is restricted to the bottom region of the crystals, whereas the precipitates are identified to be the origin of dislocations or dislocation clusters propagating throughout the crystal during growth. As a consequence, the dislocation density in a slowly grown crystal is found to be significantly lower than in a fast grown crystal.

Der gegenwartig anfallende Akkumulatorenschrott besitzt hohere Zinngehalte als die Bleilegierungen moderner Akkumulatoren. Dadurch fallen bei der Aufarbeitung des Akkuschrotts blei/zinnhaltige Raffinationsprodukte an, die nicht in den Wertstoffkreislauf zuruckgefuhrt werden konnen. Es wird eine Moglichkeit zur Trennung dieser Produkte beschrieben. Damit hat der Recycler die Moglichkeit, die Wertstoffe Zinn und Blei der Wirtschaft wieder getrennt zur Verfugung zu stellen. The currently incoming battery scrap contains higher tin concentrations than modern starter batteries. The lead and tin containing mixtures, which are generated in recycling of this scrap, cannot be returned into the cycle of recoverable materials. This report describes a method to separate the constituents of the mixtures in order to return lead and tin into the economic cycle.

A novel approach to deposit GaN layers directly on a sapphire substrate by Hydride Vapor Phase Epitaxy is presented. The two-step deposition process includes the growth of GaN nucleation layers at intermediate temperatures in the range of 750 – 900 °C and subsequent high-temperature overgrowth at about 1040 °C. Closed and non-closed nucleation layers with a thickness of up to 2 μm were produced and characterized by scanning and transmission electron microscopy, micro-Raman spectroscopy and X-ray diffraction. A growth temperature of 780 °C is found to be optimal with respect to density and size distribution of nucleation islands. Raman measurements performed on the nucleation layers reveal nearly zero residual stress indicating effective stress relaxation on cooling down from growth temperature. The results of first overgrowth experiments demonstrate the possibility to grow 10 μm thick, crack-free GaN layers of high crystalline quality on the nucleation layers. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work a fixed-grid, virtual-front tracking model originally developed for modeling dendritic growth has been adopted for transient simulations of dopant segregation in vertical gradient freeze (VGF) melt growth of Ga-doped germanium under the influence of a rotating magnetic field (RMF). The interfacial Stefan conditions for temperature and solute are formulated in volumetric terms in energy and solute conservation equations, which allow the interface to be tracked implicitly with no need to calculate the growth velocity. The model and the code are validated against an analytical solution for the transient solidification of a binary alloy at constant velocity. The numerical results show the strong relationship between the melt flow pattern and the dopant concentration in the crystal grown. The better melt mixing during growth under the influence of RMF is found to have a significant impact on the axial and radial macrosegregation of dopants. Simulation results are in good qualitative agreement with previous experimental observations of the dopant segregation in VGF-RMF growth, which now are seen ass a direct consequence of the mixing state of the melt.

An experimental study of the correlation between dislocations, grain orientation, and grain boundaries in multicrystalline silicon (mc-Si) bulk crystals is presented. Selected mc-Si samples revealing typical structural patterns like clustering or line-up of dislocations in the vicinity of grain boundaries are measured by electron backscatter diffraction (EBSD). The orientation of dislocation slip planes and twin boundary planes as well as the relationship between the misorientation of neighbouring grains and the spatial alignment of dislocations are analyzed on the basis of the relevant pole figures calculated from EBSD scans. The effect of grain boundaries on the behaviour of dislocations seems to be related to the presence or absence of a common slip system on both sides of the boundary and hence, to the type of lattice misorientation between involved grains. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In the present paper the effect of the furnace interior materials on the carbon and oxygen concentrations in multicrystalline silicon (mc-Si) is studied. Mc-Si ingots were produced in a high-vacuum induction furnace by means of the vertical Bridgman technique. Growth experiments with or without graphite components in the furnace as well as with crucible coatings of different oxygen concentrations were performed. The concentration of carbon monoxide in the growth chamber is found to depend significantly on the setup used. A standard, graphite-containing setup results in pronounced CO formation, which can be completely suppressed by applying graphite-free elements. Oxygen in the crucible coating is shown to influence the concentration of carbon monoxide via the formation of SiO. Growth under a CO enriched atmosphere is associated with the formation of a SiC/SiO2 melt surface layer, which pins the carbon concentration in the melt or crystal near its solubility limit, whereas in graphite- or CO-free growth the dissolved carbon segregates approximately according to Scheil’s law. On the other hand, the effect of carbon monoxide on oxygen concentration in the grown crystals appears to be negligible. Instead, the oxygen concentration is directly related to the oxygen content of the crucible coating.

Numerical and experimental results on the thermal optimisation of vertical gradient freeze crystal growth are presented. An inverse modelling approach is described aimed at solidification with a constant growth rate and planar solid–liquid interface. As a result of modelling an optimised growth process characterised by a modified ampoule configuration and thermal regime was established. For experimental confirmation Ga-doped germanium single crystals were grown with the optimised process. In good agreement with the numerical results, solidification with an almost constant growth rate was achieved with the interface deflection being significantly lower than in conventionally grown crystals.

The influence of the CO concentration in the gas phase on the distribution of carbon in Bridgman-grown, multicrystalline silicon is studied. The growth experiments were conducted in a high-vacuum induction furnace either under a CO enriched atmosphere or under CO free conditions. Furthermore, thermodynamic calculations in the system silicon/oxygen/carbon were done. In crystal growth under a CO enriched atmosphere a SiC-containing layer is formed on the top surface of the melt in agreement with the calculated phase diagram. In this case, the level of substitutional carbon in the cystal was found to be almost constant, whereas the axial carbon concentration in crystals grown under CO free conditions increases monotonously according to Scheil's law.

Ethanol is well suited as an energy carrier for fuel cells as it has a high energy density; it is non toxic and simple to transport and store. If used in SOFCs, one major task is to produce synthesis gas from it with a high percentage of H2 and CO. Dry partial oxidation (POX) is the simplest reforming principle for SOFCs. Thermodynamic calculations showed that simple SOFC setups should be possible with an ethanol POX reformer. Thermodynamic equilibria of ethanol partial oxidation were calculated with respect to coke formation. It has been shown that with air ratios above λ = 0.28 and 96 Vol% ethanol / 4 Vol% water sooting does not occur for temperatures above 700{degree sign}C. Currently, the most important task is to identify effective catalysts for the partial oxidation of ethanol. Experiments with low cost base metals like nickel on aluminium oxide showed great promise for ethanol conversion.

In this paper experimental results of the radial dopant segregation in Ge:Ga single crystals grown by the vertical gradient freeze technique with a rotating magnetic field are presented. The segregation is analysed on the basis of the carrier concentration measured by means of Hall effect and Fourier transform infrared (FTIR) spectroscopy. In growth without the field the carrier concentration increases towards the axis, whereas much more uniform radial concentration profiles are found in crystals grown under the influence of the rotating field indicating a pronounced impact of the melt flow on the dopant segregation. Apparently, the accumulation of the Ga solute near the centre of the melt during growth under natural buoyancy is reduced by the electromagnetically induced flow. This phenomenon is discussed with respect to analytical and numerical results published recently.

This paper presents a one-dimensional steady state model of a solid oxide fuel cell (SOFC) to be used in an Auxiliary Power Unit (APU). The fuel cell is fed a prereformed gas from an external autothermic reformer. In addition to the three electrochemical reactions (reduction of oxygen at the cathode, oxidation of hydrogen and carbon monoxide at the anode) the water–gas shift reaction and the methane steam reforming reaction are taken into account in the anode channel. The model predicts concentrations and temperatures and uses an equivalent circuit approach to describe the current–voltage characteristics of the cell. The model equations are presented and their implementation into the commercial mathematical software FEMLAB is discussed. An application of this model is used to determine suitable operating parameters with respect to optimum performance and allowable temperature.

In Metallgewinnungselektrolysen werden verschiedene Bleilegierungen als unlosliche Anoden eingesetzt. Wesentliche Forderungen an das Anodenmaterial sind eine niedrige Korrosionsrate zur Erhohung der Lebensdauer, eine niedrige Sauerstoffuberspannung zur Senkung des spezifischen Energiebedarfs und eine gute mechanische Stabilitat. Zur Verbesserung der Anodeneigenschaften wurden in den letzten Jahren die Herstellungsbedingungen und die Gehalte an Legierungselementen optimiert. Ein Teil dieser Entwicklungen wurde aus Untersuchungen zur Verbesserung der Eigenschaften von Gittermaterialien fur Bleiakkumulatoren ubernommen. In der Kupfergewinnungselektrolyse wurden die PbSb-Anoden weitgehend durch PbSnCa-Anoden ersetzt. Diese Anoden haben gute mechanische und Korrosionseigenschaften, aber ein relativ hohes Anodenpotenzial. In der Zinkgewinnungselektrolyse werden bis heute PbAg-Anoden verwendet.

Copper is one of the major metallic materials together with steel and aluminum. At present, approx. 11 Mt of copper are produced all over the world by electrorefining in sulfuric acid electrolytes. In the last years the current density could be increased to 320-340 A/m 2 by simultaneous improvement of the cathode quality, although the parameters electrolyte and anode quality did not change essentially. This was possible substantially by modifying the cell design, the starter sheets and the optimization of inhibitors and flow control at the electrodes. Further possibilities to optimize this process are described in this paper.

An electrolytic process is applied to the de-metalization of rinse waters emerging from nickel-plating baths. Optimum conditions of nickel recovery from this type of solution have been investigated through a series of experiments carried out in a rotating packed cell (Rollschichtzelle®). The effects of temperature and pH of electrolyte, current density, cell rotation speed, and diameter of the cathode granules were examined. Ninety percent of the nickel was recovered from a solution of 450 mL volume, with a pH of 5.5±0.05, 2 g/L initial nickel concentration, and by using cathode granules of 5 mm in diameter. At 50 °C electrolyte temperature and 325 A/m2 current density, 74% current efficiency was attained with 4.2 kWh/kg Ni energy consumption.

Polyethylene glycols (PEGs) with well-defined molecular weight ranges are interesting alternative additives for copper electrorefining. In comparison to glue, PEGs offer high thermal stability and slow chemical decomposition at higher temperatures, with high cathodic polarization. Thosefactors are advantages for an optimized process control in copper electrorefining. Investigations into cathodic polarization as a function of molecular weight and concentration at 500 A/m2, and also into the half-life of PEGs, were conducted in typical copper electrolyte.

A novel, vertical Bridgman-type technique for growing multi-crystalline silicon ingots in an induction furnace is described. In contrast to conventional growth, a modified setup with a cone-shaped crucible and susceptor is used. A detailed numerical simulation of the setup is presented. It includes a global thermal simulation of the furnace and a local simulation of the melt, which aims at the influence of the melt flow on the temperature and concentration fields. Furthermore, seeded growth of cone-shaped Si ingots using either a monocrystalline seed or a seed layer formed by pieces of poly-Si is demonstrated and compared to growth without seeds. The influences of the seed material on the grain structure and the dislocation density of the ingots are discussed. The second part addresses model experiments for the Czochralski technique using the room temperature liquid metal GaInSn. The studies were focused on the influence of a rotating and a horizontally static magnetic field on the melt flow and the related heat transport in crucibles being heated from bottom and/or side, and cooled by a crystal model covering about 1/3 of the upper melt surface.

The high temperature vapor phase epitaxy (HTVPE) uses ammonia and thermally evaporated, elemental gallium as precursors for the growth of GaN films. This paper investigates the HTVPE using numerical modeling of the gallium vapor transport and systematical growth experiments. The presented growth setup allows a flexible control of the growth process and variation of growth parameters in a wide range. Based on simulation results, the impact of the gallium melt temperature, the gas flow in the reactor and the reactor pressure on the gallium vapor transport is studied in detail. Experimental growth rates as function of the reactor pressure and the melt temperature are compared with the numerical simulation. The influence of hydrogen in the carrier gas on the properties of the HTVPE GaN layers is discussed.

The influence of a rotating magnetic field (RMF) on the vertical gradient freeze (VGF) growth of Ga-doped Ge is studied numerically using the program CrysVun ++ . On the basis of a global, time-dependent simulation of the VGF process including the melt flow a simple approach to estimate the solute segregation is presented. It is shown that the radial as well as the axial segregation can be improved by applying a RMF.

Results on the experimental and numerical modelling of the melt flow typically observed in vertical gradient freeze (VGF) crystal growth with a travelling magnetic field (TMF) are presented. Particular attention is paid on the transition from a laminar to a time-dependent flow, which represents a crucial problem in VGF growth. Low-temperature model experiments at around 80 °C were performed using a GaInSn melt in a resistance furnace with concentric, separately adjustable heating zones. The TMF was created by an external coil system, and the flow velocity was measured by means of the ultrasonic Doppler velocimetry (UDV). The melt flow was simulated numerically using a finite volume code based on the open source code library OpenFOAM. As a criterion for the stability of the flow the turbulent kinetic energy was calculated under the influence of the TMF and thermal buoyancy. The results obtained are compared to isothermal TMF flow modelling at ambient temperature. The stability limit of the melt flow is found to be significantly influenced by the mutual interaction of buoyant and TMF-driven flows. Both experimental and numerical results show the stabilizing effect of natural, VGF-type buoyancy on the TMF-induced flow.

Experimental results on the vertical gradient freeze growth of germanium single crystals without crucible contact are presented. Two different approaches to establish a stable pressure difference necessary for avoiding the contact between crystal and crucible on solidification are described. Germanium crystals with a diameter of up to 3 in were grown almost without contact to the crucible wall. The effect of detachment is discussed with respect to the microscopical surface roughness and dislocation density of the grown crystals. In comparison to conventionally grown reference crystals the structural perfection of the detached-grown crystals is found to be much higher which can be attributed to the reduced thermal and thermo-mechanical stress in growth without wall contact.

Experimental and numerical results are presented demonstrating the impact of a traveling magnetic field (TMF) on the heat and mass transport in doped, VGF-grown Ge crystals. In growth with TMF a considerable effect on the deflection of the solid–liquid interface is observed, whereas the dopant segregation does not change significantly compared to the growth without field. Furthermore, pronounced striation patterns were found in the crystals indicating a time-dependent melt flow during growth. A combined TMF/DC field is presented which was developed to avoid this effect. Isothermal model experiments using a liquid GaInSn alloy show the capability of the DC field for an effective damping of fluctuations of the flow velocity in qualitative agreement with numerical results.